/Engine/Source/Editor/UnrealEd/Public/EditorViewportClient.h
Helper function to calculate the safe frame rectangle on the current viewport
bool CalculateEditorConstrainedViewRect ( [FSlateRect](API\Runtime\SlateCore\Layout\FSlateRect) & OutSafeFrameRect, [FViewport](API\Runtime\Engine\FViewport) * InViewport, const float DPIScale )